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  #1  
Old 05-05-2006, 11:53 AM
Cabernet red, actually
 
Join Date: Jan 2006
Location: Willamette Valley, OR
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Tranny-Can extra fluid compensate for vac?

I discovered yesterday that not only is my vac line to the transmission disconnected, but it has almost certainly never been connected since I bought the car in January. I NEVER suspected this because the shifting isn't that rough and I had enough vacuum in the system for locks, shutoff, etc. I think this is because the disconnected end of the trans. vac line was filled with oily gunk that basically served the same purpose as a golf tee.

My first two upshifts tend to be hard but they're not that hard, and they do better in warm weather. Sometimes when I first start the car for the day the third upshift won't occur until 4200 rpm, but it shifts fine after that.

Given what I've read about vacuum and trannsmissions, I would expect harder shifts than I have and downshifts that I can feel.

I think my transmission fluid is high but I'm uncertain due to the inexact nature of using the dipstick (I started a thread on that a few days ago).

This tranny may still be under warranty as it was rebuilt last July. The warranty was good for a year but the shop has changed ownership, I think. In any event I feel that I really need to know what I'm talking about before I bring it in. Could too much tranny fluid compensate somewhat for a loss of vacuum? That is the big question I have right now. If anyone can shed some light on what they think is going on, it will be much appreciated.

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1985 300D Turbo, CA model
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  #2  
Old 05-05-2006, 11:56 AM
boneheaddoctor's Avatar
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NO..........if you run too much fluid you risk foaming....and you know foam does a poor job of conveying hydraulic pressure and lubrication.

Too much = bad

Too little = bad
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Old 05-05-2006, 12:30 PM
Cabernet red, actually
 
Join Date: Jan 2006
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Just to clarify, I want to get my transmission so that it is running according to spec. I'm just really, really surprised it works as well as it does with no vacuum and I wonder why that is. If I were certain I had too much fluid I would have drained some out by now, but the seemingly inexact nature of the dipstick makes me uncertain about the fluid level.
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  #4  
Old 05-05-2006, 12:34 PM
boneheaddoctor's Avatar
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Vacuum on the 300 series transmissions is there to soften shifts. (except for certain 240D transmissions that use vacuum to firm up shifts)

that will explain why it works so well.
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Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
---------------------
Section 609 MVAC Certified
---------------------
"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche
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  #5  
Old 05-05-2006, 12:59 PM
Cabernet red, actually
 
Join Date: Jan 2006
Location: Willamette Valley, OR
Posts: 503
Quote:
Originally Posted by boneheaddoctor
Vacuum on the 300 series transmissions is there to soften shifts. (except for certain 240D transmissions that use vacuum to firm up shifts)

that will explain why it works so well.
My understanding is it is there to soften all the shifts. It's only the first couple of upshifts that are hard, though, and if I'm careful with the throttle they're not even that hard. So this is what's confusing to me. I guess maybe I thought the vacuum has a greater impact on the tranny than it actually does?

Thanks for your help, bone.
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1985 300D Turbo, CA model
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  #6  
Old 05-05-2006, 01:06 PM
boneheaddoctor's Avatar
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Quote:
Originally Posted by Maroon 300D
My understanding is it is there to soften all the shifts. It's only the first couple of upshifts that are hard, though, and if I'm careful with the throttle they're not even that hard. So this is what's confusing to me. I guess maybe I thought the vacuum has a greater impact on the tranny than it actually does?

Thanks for your help, bone.
No problem....there is a caveat however for those reading this thread with 240D automatics as that vacuum is very important to avoid flairing and slipping on those models.
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Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
---------------------
Section 609 MVAC Certified
---------------------
"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche
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  #7  
Old 05-05-2006, 02:35 PM
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Did you check the fluid with the tranny hot and idling in park?
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  #8  
Old 05-05-2006, 03:05 PM
Cabernet red, actually
 
Join Date: Jan 2006
Location: Willamette Valley, OR
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Quote:
Originally Posted by Diesel Giant
Did you check the fluid with the tranny hot and idling in park?
I've checked it several times, each time with it idling in park. First, I checked it cold and it appeared to be several inches too high on the dipstick. I thought this was odd since the owner's manual says it will be about 12 mm below the 'low' line if cold. But then I read on here that when it's cold it will read high.

Then I checked it after driving a couple of miles. I shifted through all the different modes (R,D,S, etc.), still high. then I read here that a couple of miles won;t get the tranny fluid warmed up enough.

Then I drove about 13 miles and checked it the same way; still 1 1/2 inches high. Then I read that some people recommend driving about 20 miles and letting it idle for several minutes before checking. I have yet to try it this way.

When I do check it there are generally a few bubbles, but nothing that looks foamy or frothy.

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